Automatic dead-reckoning device



Oct. 14, 1947.

FIG. I

REDUCTDN GEAR 80X weer/oh GEAR 00! w. P. ALBERT AUTOMATIC DEAD RECKONING DEVICE Filed Sept. 7, 1944 AMPLIFIER AND DETECTOR N5 jg ntoucr/o/v cam sax 2 Sheets-Sheet 1 INVENTOR By W I? ALBERT ATTORNEY 1947: j W.'P. ALBERT AUTOMATIC DEAD RECKQNING DEVICE 2 Sheets-Sheet 2 Filed Sept. 7, 1944 A TTORNE Y Patented Oct. 14, 1947 UNITED STATES PATENT OFFICE AUTOMATIC DEAD REC K Q Nl NG Walter P. Albert, Madison, .N. J assignorto Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application September 7, 1944, Serial No. 552,381 7 Claims. (01. 235-51) This invention relates to an air position indicator for use on an aircraft for enabling the pilot or navigator to determine at any instant the latitude and longitude of his position and the air miles he has flown from any specified take-oil point.

More particularly, the invention is concerned with the provision of electrical equipment for controlling indicators which continuously indicate the aircraft position in degrees and minutes of latitude and longitude and the air miles which have been flown. The utility of apparatus of this character is quite evident. On ships the problem of determining the ships position at any instant is not diflicult due to the slow speed at which surface ships sail and due to the fact that suchships always carry a navigator as a member of the crew who has ample time to make celestial observations, to do the navigational plotting that is necessitated from the data secured from such observations and to keep the necessary records of course and speed to enable a dead-reckoning position to be always known. However, aircraft and particularly airplanes whichhave high cruising speeds present a more diificult problem for solving navigational data, to determine positions. This is particularly true of airplanes of the high speed type which may not have space to accommodate a navigator aspart of the crew, Furthermore, in aerial navigation under war conditions evasive action involves such frequent changes of course and speed that a navigator cannot keep an accurate log from which the dead-reckoning position may be obtained. The apparatus which is the subject of this invention may be described as an automatic deadreckoning device.

Most modern airplanes are provided with a source of LOO-cycle 26-volt alternating current for the operation of remote controlled instruments and with a source of 26-volt direct current. However, some types of airplanes, while having a source of 26-volt direct current, do not have a source of LOO-cycle alternating current and other types of planes which are provided with such an alternating current source do not have a source of adequate capacity to carry the extra load which would be imposed thereon by the installation of air position indicator apparatus of the alternating current type. It is therefore one object of the present invention to provide apparatus operative by direct current which will continuously-indicate the latitude and longitude of the air position of the airplane in which it is installed and the number of air miles flown.

t is a further object of theinvention to pro-' vide in such an air position indicator apparatu remote control circuits whereb the indicating instruments may beso compactly assembled that they may be mounted on the instrument panel of an airplane and wherebythe cireuitsand apparatus for controlling such instruments may be located remotely ,therefromin any location in the airplane where mounting space is available.

To attain these objects, apparatus has been designed in two parts, an indicating unit and a control unit. Most modern airplanes are equipped withan air mileage unit and witheither a remotecontrol earthinductor compass known as a (flux gate compass or a remote control magnetic compass known as a magnesyn compass. From theseunitsinformation may be secured concerning the airspeed andthe truecompass course of the airplane flight for enabling the controlunit ,tocontrol the indicator unit. The indicator unit may be orthe type disclosed schematically inthe application Serial No, 527,999 of W. H. T. Holden, filedMarch 24, 1944, or may be of the type disclosed inthe application Serial No. 538,529 or w. H. T. Holden, filed June 2, 194.4. Theindicator unit is provided. with three indi cators ofthecounting wheel type, one of which is controlled to indicate the air miles flown, the second of which indicates the degrees and ,m.inutes of latitude of the instant position ofthe air plane and the third of which indicates the degrees and minutes of the longitude of theinstant position of the airplane. A compass rose and pointer may also be providedfor indicating the true compass course of the flight. Provision is made for enabling the latitude and longitude indicators to bereset to indicate the latitude and longitude of the position of the airplane atsome known point, as ,fq fixample, at the take-off of a flight and withmeans iorenabling the indicators to be operated in one or the other directiondependent on whether the flight is being conducted in the north or south hemisphere or east or west of a particular reference meridian.

In order that the indicator unit may be sufliciently compact so that it may be mounted in the usual instrument panelin front of the pilot, each indicator is arranged to be operated by a stepping mechanism individual thereto, the step ping mechanisms associated with the latitude and longitude indicatorsbeing operable to advance the indicators step-by-step in one or the other direction. The stepping mechanism associated with the air miles indicator is effective to advance such indicatorin but. one direction of rotation.

The control unit comprises a latitude impulse generator, a longitude impulse generator and a secant variator for varying the number of impulses delivered from the longitude impulse generator to the longitude indicator. The latitude and longitude generators each comprises a drum having twelve triangularly shaped conducting segments embedded in the insulating surface thereof and arranged in two circumferential series as disclosed by the development of the drum surface disclosed in Fig. 3. These drums are both rotated at a speed commensurate with the air speed of the flight through a reduction gear box from the air mileage unit of the airplane. For engagement with each of these drums, three brushes are provided two of which are fixed and engage continuously with the two series of conducting segments respectively and serve as take-01f brushes and the third of which is movable axially along the surface of the drum.

The movable brushes of the latitude and longitude impulse generators are movable axially along the surfaces of the drums by Scotch yokes which are driven by a servo-motor operable in accord ance with the true compasscourse of the flight.

hrough one Scotch yoke, the movable brush of the latitude impulse generator is advanced axially along the drum in accordance with the cosine of the true course angle and through the other scotch yoke the movable brush of the longitude impulse generator is advanced axially along the surface of the drum in accordance with they sine of the true course angle. Interposed in the circuits extending to the movable brush of each impulse generator is a pair of contacts operable by a cam driven through step-up gearing having a ratio of l to 60 from the associated drum driving shaft whereby the contacts are closed sixty times during each revolution of the drum. Because of the arrangement of the conductive segments of each drum, the movement of the movable brush the cam operated contacts, it is possible to generate from one to sixty impulses during each revolution of the drum, dependent upon the position of the movable brush, and the generated impulses may be transmitted over one or the other of the fixed take-on brushes dependent upon whether the movable brush is advanced into engagernent with one or the other series of conductins segments.

In response to the rotation of the drum of the latitude impulse generator at a speed commensuwith the air speed of the airplane flight, and the movement of the mol'able brush associated with such drum axially along the surface of the drum to an amount commensurate with the cosine of the true compass course of the flight, the latitude impulse generator generates impulses in accordance with changes in the latitude of the flight course and transmits such impulses to the latitude indicator.

Also rotatable by step-up gearing from the shaft of the longitude impulse generating drum is a secant variator having a speciall contoured conducting segment embedded in the insulating surface of its drum, a fixed brush engaging the conducting segment for connecting one terminal of the direct current power source to such segment and a brush movable axially along the drum to an amount commensurate with the indicated latitude of the instant position. The movable brush is connected over the cam operated contacts associated with the longitude impulse generator with the movable brush of such generator so that due to the movement of the brush and the rotation of the drum of the secant variator, the rotation of the longitude impulse generator drum at a speed commensurate with the air speed of the airplane flight and the movement of the movable brush associated with the latter drum axially along the surface thereof to an amount commensurate with the sine of the true compass course of the flight, the longitude impulse generator generates impulses in accordance with changes in the longtiude of the flight course and transmits such impulses to the longitude indicator.

Through an additional reduction gear box, the air mileage unit of the airplane is also effective to cause the closure of a pair of cam-operated contacts once for each nautical mile flown to transmit impulses to the air mileage indicator.

The servo-motor for operating the Scotch yoke is also effective through telemetric control to operate the true compass course indicator of the indicating instrument and is controlled from a flux gate compass control unit through a compass servo amplifier and detector circuit in a wellknown manner as will hereinafter be described.

For a clearer understanding of the invention and the mode of its operation, reference may be had to the following detailed description thereof when read in connection with the accompanying drawings in which:

Fig. 1 shows the control apparatus of the air position indicator of the present invention and the manner in which it is controlled from the air mi'eage motor unit and the flux gate compass unit of an airplane;

Fig. 2 shows schematically the apparatus and circuits of the air position indicator unit;

Fig. 3 shows a development of the circuit of the drum of either the latitude or longitude impulse generator;

Fig. 4 shows a development of the surface of the drum of the secant variator; and

Fig. 5 is a vector diagram explanatory of the theoretical aspects of the invention.

The indicator disclosed in Fig. 2 includes two two-directional stepping devices STPI and STPZ and a single directional stepping device STP3. The stepping devices STPI and STPZ may be of any suitable type, for example, of the type disclosed in Patent No. 2,323,840, granted July 6, 1943, to T, ObsZarny. The stepping device STPI comprises a single ratchet wheel 20!] with which two stepping pawls 20! and 202 cooperate. The pawl 20! is operable by the stepping magnet 233 to advance the ratchet wheel 200, for example, in a counterclockwise direction and the pawl 202 is operable by the stepping magnet 204 to advance the ratchet wheel 20!! in the opposite direction. The ratchet wheel 2% of the stepping device STPI is mounted upon the input shaft 205 of the reduction gear box 266 which is connected by the reduction gears 20! having a reduction ratio of 1 /2:l to the input shaft 208 of the latitude counter LC. If it is assumed that the ratchet wheel 260 has forty teeth and is advanced one step for each minute change in latitude, then through the reduction gears 201, the input shaft 288 of the counter LC will be advanced onesixtieth of a revolution and thus the input wheel of the counter, which is graduated 0 to 59 minutes, is rotated one revolution for each degree of latitude. The other wheels of the latitude counter are advanced by decimal Geneva movements in the usual manner to register the units and tens of the degrees of latitude.

Mounted on the output shaft 209 of the reduction gear box 206 is a pinion 'IIlI which meshes with arack I02. To the rack I02 is attached the movable brush I63 of the secant variator SV.

The input shaft 268 of the counter LC also carries a bevel gear 2| 0 which may be meshed with the setting gear 2H when the setting knob 2I2 is pushed inwardly against the tension of spring 2I3. With the gears 2H] and 2H meshed the rotation of the knob 2I2 is effective to set the counter LC at a definite fix or land mark the latitude of which is known. When the knob 2I2 is pushed in to reset the counter LC, the spring 2I3 disengages its normal contact to disconnect battery B from the windings of stepping magnets 203 and 264 so that such magnets are ineffective during the resetting operation.

When a flight is being conducted in the northern hemisphere, the stepping control conductors 2I4 and 2I5 are connected over the normal contacts of key KI to the windings of magnet 203 and 204, respectively, of the stepping device STPI so that the counter LC will increase its reading as the flight proceed northward and will decrease its reading if the flight proceeds southward towards the equator. When the equator is crossed, a reading of 00 degrees 00 minutes would be followed by a reading of 99 degrees 59 minutes as the flight proceeds into the southern hemisphere. In order therefore that the counter may increase its reading through 00 degrees 01 minute, etc., the key KI is provided which when depressed directs steppin impulses incoming over conductor 2 I4 to magnet 294 rather than to magnet 2G3 and directs stepping impulses incoming over conductor 215 to magnet 203 rather than to magnet 204 whereby the navigator or pilot may reverse the rotation of the counter LC as the flight crosses the equator.

The stepping device STPZ is similarly provided with a ratchet wheel 220 which is operable in a counter-clockwise direction by the stepping pawl 22I under the control of stepping magnet 223 and and in a clockwise direction by the stepping pawl 222 under the control of the stepping magnet 224. The ratchet wheel is mounted on shaft 225 which is coupled by the reduction gears 22'! which have a reduction gear ratio of 1 /211 to the input shaft 228 of the longitude counter LoC. The input shaft of the longitude counter is rotated through one revolution by sixty steps of the stepping device and thus rotates the input wheel of the counter, which is graduated 0 to 59 minutes, one revolution for each degree of longitude. The other wheels of the longitude counter are advanced by decimal Geneva movements in the usual manner to register the units, tens and hundreds of the degrees of longitude.

The input shaft 228 also carries a bevel gear 230 which may be meshed with the setting gear 23I when the setting knob 232 is pushed inwardly against the tension of spring 233. With the gears 230 and HI meshed, the rotation of the knob 232 is effective to set the counter LoC at a definite fix or land mark, the lon itude of which is known. When the knob 232 is pushed in to reset the counter LoC, the spring 233 disengages its normal contact to disconnect battery B from the windings of stepping magnets 223 and 224 so that such magnets are ineffective during the resetting operation.

When a flight is being conducted in the eastern hemisphere or east of the reference meridian, the stepping control conductors 234 and 235 are connected over the normal contacts of key K2 to the windings of magnet 223 and 224, respectively, of

the stepping device STPZ, so that the counter LoC will increase its reading as the flight proceeds'eastward and will decrease its reading if the flight proceeds westward toward the reference meridian. This counter may read 00 degrees 00 minutes to degrees 00 minutes. When the 180 degree reference meridian is crossed a reading of 180 degrees 00 minutes would be followed by 180 degrees G1 minute as the flight proceeds into the western hemisphere. In order therefore that the countermay decrease its reading through 179 degrees 59 minutes, etc., the key K2 is provided which when depressed directs stepping impulses incoming over conductor 234 to magnet 224 rather than to magnet 223 and directs stepping impulses incoming over conductor 235 to magnet 223 rather than to magnet 224 whereby the navigator or pilot may reverse the rotation of the counter as the flight crosses the reference meridians O and 180.

The ratchet wheel 2'36 of the stepping device STP3 is rotatable in but one direction through the operation of the stepping pawlZSI under the control of the stepping magnet 238. This ratchet wheel has ten teeth and is mounted on the input shaft 239 of the air miles indicator AMC, the input wheel of which is graduated 0 to 9 and moves step-by-step making one revolution per each ten nautical miles of flight. The other wheels of this counter are advanced by decimal Geneva movements in the usual manner to reg ister the tens, hundreds and thousands of miles.

The compass indicator C is provided with a dial having a compass rose thereon, a compass pointer 24:] driven by the shaft 24I connected to the rotor of the synchro-receiver SRi for indicating the true compass course of the flight and a correction pointer 242 driven by the sleeve shaft 243 through the gear 244 and pinion 245 from the shaft 246 which is rotatable by the correction knob 241.

The output shaft IE5 of the air mileage unit AMU of the airplane is connected directly to the input of the reduction gear box Iil'I the output shaft of which gear box is connected to shaft I98. The shaft I08 drives the shaft I59 through unity ratio bevel gears H3. Mounted on the shaft I09 and driven thereby is the drum III of the latitude impulse generator LG with which two fixed brushes H2 and H3 and a movable brush H4 cooperate. The drum III may be molded from insulating material or have a surface of insulating material in which are embedded twelve triangularly-shaped conducting segments mounted in two circumferentially arranged series as best disclosed in Fig. 3, which figure shows a development of the surface of the drum II I. All of the segments have their leading edges positioned parallel to the axis of the drum and are of equal length.

It will be noted from Fig. 3 that the lowermost segments H5 and H5 are positioned in the surface of the drum III with their apices spaced apart only slightly more than the width of the brush I I4 so that if the flight course is absolutely due north the brush H4 will be engaged by neither segment H5 nor H6 but will be engaged upon the slightest movement of the brush I I4 indicative of a deviation to the east or west from a due north course of flight. If it be considered that the length of the leading edge of each segment is equal to sixty increments of movement of the brush H4 then the apices of the succeeding segments H8. I20, I22, I24 and I25 of the right-hand series of segments, as viewed in Fig.

3, are successively advanced toward the right end of the drum by the width of one such increment and similarly the apices of the succeeding segments H1, H9, 12!, I23 and I25 of the left-hand series of segments are successively advanced toward the left end of the drum by the width of one such increment. Therefore, for example, if the brush 5 I4 is advanced toward the right it will be engaged first by segment H6 and then as it moves a distance equal to one increment it will be engaged by both segments I I5 and I I8 during each revolution of the drum. If the brush is advanced a further increment it will be engaged by segments H5, H8 and I 29 during each revolution of the drum and as the brush further advances, for example, to a distance equal to five increments it will be engaged by all of the segments of the right-hand series during each revolution. And, since the width of the segments increase toward the right, the duration of engagement of each segment with the brush H4 will increase as the brush moves toward the right.

The segments of each series are joined at their wide or outer ends to form a continuous slip ring, the fixed brush H2 engaging with the slip ring of the right-hand series of segments and the fixed brush i I3 engaging with the slip ring of the lefthand series of segments.

The shaft I59 also has mounted thereon a gear i2! which meshes with a pinion I28 on a jack shaft 29, which latter shaft also carries the gear I35 vhich meshes with the gear I3! on the cam shaft I32. The gears I21, I28, l3!) and I3! are so designed that the cam shaft I32 makes sixty revolutions for each revolution of the drum III. The cam shaft E32 has a cam I33 secured thereto which once during each revolution causes the closure of the contact springs I34. The drum I I I is so geared to the air mileage unit AMU that it rotates in the direction indicated by the arrow in Fig. 1 so that as it rotates the leading edges of the conducting segments such as I I8 approach the brush H4 and the geared connection of the cam I33 with the shaft I 99 is so adjusted that the cam operated springs I 34 always close just subsequent to the engagement of the leading edge of any drum segment with the brush I i4. Since the drum segments may be made of base metal this arrangement insures that the impulse circuit which extends from the grounded terminal of the battery over the contact springs I34, over brush H4 and a segment of the drum III, will always be made at the precious metal contacts of the springs I34, thus preventing arcing and pit ting of the drum segments.

If the brush H4 is moved so that it is just barely engaged by the tip of a segment, such as I I8, such engagement may not be of suflicient duration to enable the completion of an impulsing path from ground over the contacts of spring I34, brush H4, segment IE5, brush I I2, conductor 2H5, the left normal contacts of key K! and battery through the winding of steppin magnet 252 of the stepping device STPL If, however, the brush H4 moves slightly more its engagement by seg ment I it may be of such duration as to enable an impulse to be transm' ted but the brush ma not have been moved suiiiciently to be engaged by the tip of segment H8 so that only one impulse would be transmitted during each revolution of the drum III. As the brush H4 advances it may become engaged. not only by segment H6 but by segment H3, but if it is engaged only b the tip of segment H8 the duration of the engagement may not be sufiicient to cause the transmission of an impulse and consequently the only impulse per revolution would result from the engagement of segment H6 with brush II4 but, upon a slightly further advance of the brush II4, the duration of engagement of brush II4 with segment H8 would be increased to become coincident with the closure of contact springs I34 thereby resulting in the transmission of two im-- pulses per revolution of the drum, one at the time of the engagement between brush H4 and segment H5 and the second at the time of engagement of brush H4 and segment I I8. As the brush H4 advances further, additional impulses per revolution will be transmitted and when the brush has been advanced to a position such that circuit closures at the springs I34 coincide with the engagement between brush H4 and segments I20, I22, I24 and I26 six equally spaced impulses will be transmitted during each revolution of the drum. In this position of the brush I I4 the trail ing edge of the segment H5 will leave the brush H4 before the contact springs I34 will close a second time during the engagement of brush I 4 with segment I I6.

As the brush advances further to be engaged by a wider portion of the segment H4 two closures of the contact springs I34 will occur while the segment I i8 is in engagement with the brush H4 and consequently a total of seven impulses will be transmitted during each revolution of the drum III. In this manner as the brush moves further the number of impuls s transmitted during each revolution will increase until when the brush has moved to the extreme of its movement it will be engaged by the widest portion of each of the segments and ten closures of the contact springs I34 will occur as each segment passes the brush H4 resulting in the transmission of sixty impulses during each revolution. It will be obvious that impulses varying from one to sixty would be transmitted in the same manner upon the movement of the brush H4 from its central position toward the bottom end of the drum III as viewed in Fig. 1, over a circuit extending from ground over the contact springs I34, brush H4, segments H5, H1, etc, brush H3, conductor 224, the right normal contacts of key KI and to battery through stepping magne 293 of stepping device STPI.

It therefore follows from the arrangement of the segments on the drum 5 i I that the closure of the interrupter contacts 234, counted 1 to 60, during each revolution of the drum will occur as the brush engages successive segments in the order 1-l12l-3l4151 and impulses will be transmitted whereas the closure of the interrupter contacts I34 which occur while the brush engages between successive segments, as, for example, closures 2 to I?) inclusive, :2 to 25), inclusive, etc., will be ineiiective and no impulses will be transmitted. This provides a more accurate counting or integrating of impulses than would be in the order 1-23 45-6. As the brush H4 moves slowly toward either end of the drum the number of effective impulses transmitted to actuate the stepping device during each revolution of the drum increases, impulses being transmitted, for example, during one revolution of the drum upon the interrupter closures l-ll21 31415l as above described, during the next revolution upon the interrupter closures 1fZ- 1l21 -314l51, during the next revolution upon the interrupter closures 1-2-1 l-12-2 l- 31--4l5l, during the next revolution upon the interrupter closures 121l12-2122-31 9 41'51, etc., until when the brush has moved to the extreme end of the drum impulses will be sent upon each of'the sixty closures occurring during a revolution of the drum.

Geared to the shaft I08 through the reduction gear box I35 is a camshaft I36- upon which is secured the cam I31 for operating the contact springs I19. The ratios of the gear boxes I01 and I35 are such that the cam I31 is driven from the air mileage unit AMU at a speed to cause the closure of the contact springs I19 once for each nautical mile flown. Thus, since the output shaft I05 of the air mileage unit AMU makes 1440 revolutions per nautical mile, the sum of the step-down gear ratios of the'gear boxes I01 and I35 should be 1440 to 1. The contact springs I19 serve to establish a stepping circuit from ground thereover and over conductor 250 through the winding of stepping magnet 238 of the stepping device STP3- and thence to batter and ground whereby the input shaft of the air miles counter is advanced one-tenth of a revolution upon each closure of the contact springs I19 to register one nautical air mile flown.

Secured to the shaft I08 is the drum I38 of the longitude impulse generator LG. This drum is identical in construction to the drum I I I and has two fixed brushes I39 and I40 and a movable brush I4I cooperating therewith. The fixed brushes are connected over conductors 234 and 235, respectively, and over normal contacts of key K2 with the step ing magnets 223 and 224 of the stepping device STPZ. Also secured to the shaft I08 is a gear I42 which, through gears I43, I44 and I45 drives the shaft I46 on which is mounted the cam I41. These gears are so chosen that the shaft I45 and cam I41 make sixty revolutions during each revolution of shaft Hi8 and drum I38 whereby the control springs|48 are closed sixty time during each revolution of the drum I38. The shaft I08 is rotated in the direction indicated by the arrow and the gear train between the shaft I08. and the cam shaft I40 is so adjusted that the contact springs I48 close just subsequent to the engagement of the leading edge of any conducting segment of the drum I38 with the brush I4I.

Also secured to the-shaft I08 is a gear I49 which meshes with gear I50 secured to shaft II. Mounted on the shaft I5I is the drum I00 of the secant variator SV. The drum I00 may be made of insulating material or may have a surface of insulating material in which is embedded a single conducting segment I05 of the shape disclosed in Fig. i, this figure showing a development of the surface of the drum. The curved edge of the segment I05 is developed in the following manner. Referring to Fig. 5, if it be assumed that the distance FE represents L degrees of longitude at the equator, it willbe seen that an airplane flying from Fto E along the equator would have to fly 60.068 nautical miles to fly 1 degree of longitude but if the airplane were to fly a course parallel to the equator at a point nearer the earths pole fewer nautical miles per degree would have to be flown. For example. at 15 degrees latitude 58.034, at 30 degrees latitude 52.064. at 45 degrees latitude 42.546, at 60 degrees latitude 30.110 and at '75 degrees latitude 15.596 miles per degree would have to be flown. Since flight above '75 degrees latitude would not ordinarily be flown, values of miles per degree above 75 degrees latitudeneed not be taken into consideration.

The curved edge of the segment I05 is therefor determined by plotting the difference be- 10 tween the airmiles per degree at different degrees of latitude and the miles per degree at 75 degrees latitude, measured down from the top edge of the development as viewed in Fig. 4, against the degrees of latitude. The movable brush I03, when positioned at the extreme left end of the drum I00 at the time the latitude is zero or at the equator, has the shortest duration of circuit closure with the segment I05 and when positioned at the right end of the drum or when the latitude is 75 degrees the duration of the circuit closure between the brush I33 and the segment I05 will'be continuous. As previousl described the brush I03 is moved under the control of the latitude stepping device STPI. Under the control of the secant variator SV and long tude impulse generator LoG, impulses are transmitted from ground over bru h I04, segment I05 of variator SV, brush I03, cam-actuated contact springs I48, brush I4'I, segments on the drum I38 and thence over conductor 234 and over the right normal contacts of key K2 to battery through the winding of stepping magnet 223 of the stepping device STPZ or over conductor 235 and over the left normal contacts of key K2 to battery through the winding of stepping magnet 224 of the stepping dev ce STPZ dependent upon whether the brush I4I engages with the left or right series of se ments on the drum I38.

Thus the number of impu es delivered to the longitude stepping device'STP. through the operation of the ecant variator SV and the longitude drum I38 in ratio to the maximum number for a g ven setting of the longitude brush I l-I is the ratio of the metallic se ment I of the variator to the insulated se ment of the variator for the setting of the brush I03 of the variator. Also the cou ling action of the variator with respect to the lon itude drum provides an accurate method of'averaging th s ratio as applied to all segments of the drum I38;

The brushe II4 and MI are connected to Scotch yokes I52 and I53; respectively, which are both o erated by the crank pin I54 on disc I55 wh ch disc is rotated by shaft I55 driven by gears I51 and I58 from theoutput shaft IL I of the reduction gear box I60. The input shaft of the gear boxis driven by the compass servornotor SM. The shaft I55 is thus driven by the motor SM through a rotational angle corresponding to the angle of the true compass course of the flight and through the Scotch yoke I52 the brush H4 is advanced alongthe surface of the drum I I I a distance commensurate with the cosine of the true course angle and through the Scotch yoke I53 the brush MI is advanced along the surface of the drum I38 a distance commensurate with the sine of the true course angle.

The servo-motor SM is of the direct current reversible split field series-connected type and is controlled, by the three-position d fferential relay IBZ. The armature I53 of relay i252 may be operated into engagement with either its upper or its lower contact to establi h a circuit through one or the other of the field windings I64 and IE5 of the motor SM to cause the motor to run in one or the other direction under the control of the amplifier-detector I65 and thus under the control of the output of synchro-transformer STZ.

For controlling the amplifier-detector I00 and servo-motor SM the flux gate primary transmitter FPT is connectedover conductors I61, I58 and I639 with the stator windings of the differential generator DG, the Y-connected rotor windings of 11 which are connected over conductors I10, I'll and H2 with the corresponding stator windings of the synchro-transformer STE. The rotor winding R2 of the synchro-transformer is connected to the input circuit of the amplifier-detector 56 and is rotatable through the unity ratio gears t53 and 59 and through the deviation cam H3, represented by the box so labeled. by the servo-motor SM. The rotor of the dififerential generator DG is rotatable by the setting knob 24'! through the gears 248 and 243 to introduce a magnetic correction for the compass C. The gears 248 and 249 have the same gear ratio as the gears 2M and 245 so that the amount of rotation of the rotor windings of the generator DG is indicated by the correction pointer 242 of the compass C.

In order that the pilot may have an indication of the true course which he is flying the pointer 24% of the compass C is connected by shaft 26! as previously described to the rotor R! of the synchro-receiver SRI, the stator windings of which are connected over conductors it'd, I15 and H5 with the corresponding windings of the secondary transmitting generator STG. The rotor winding R of the generator STG is rotatable through the gears l5! and 58 by the servo-motor SM and the windings of rotors R and R! are interconnected by conductors ill and H8 and energized from the source of EGO-cycle current of the airplane. The rotation of the rotor winding R of the secondary transmitting generator STG by the servo-motor SM is thus instrumental in rotating the compass pointer 24?! with the magnetic correction introduced by the differential generator DG under the control of the setting knob 24'. and the correction made by the deviation cam 513. With the differential generator DG interposed between the flux gate prim ry transmit FPT and. the synchro-transformer STZ. the rotor of transformer ST?! will, through the servo-motor SM and the amplifier-detector follow the primary transmitter FPT but its position will difier by the magnetic correction angle introduced by the setting of the rotor windings of the differential generator DG as indicated by the correction pointer 242.

While the invention has been described in connection with its application to an airplane having a flux gate compass unit it is to be understood that it is also applicable to an airplane having a magnesyn type compass unit. If the airplane were equipped with the latter type of compass unit the servo-motor SM would be controlled in the manner fully disclosed in Fig. 1B of the application Serial No. 527,999 of W. H. T. Holden hereinbefore referred to.

The apparatus employed in embodying the invention having now been described, the manner in which the apparatus functions will be discussed. It will be assumed that the airplane in which the air position indicator is installed starts flight from a position of degrees 00 minutes latitude and 15 degrees 20 minutes longitude in the eastern and northern hemispheres. The pilot knows the latitude and longitude of the position of the take-cit and therefore resets the latitude and longitude counters LC and LoC by the operation of the reset knobs H2 and 232 in the manner fully described so that they indicate the position as disclosed in Fig. 2. He also sees that keys K and K2 are in positions indicative of the flight to be made in the northern and eastern hemispheres. It will also be assumed that previous to the contemplated flight, the airplane has flown 12 4367 nautical air miles as indicated by the air miles counter AMC.

It will be assumed that a flight is made in the direction indicated by the line FA in Fig. 5 with a true compass course of CN degrees as indicated by the compass C, and at such a true air speed that the distance traveled at the time an observation is made may be indicated by the vector FA. The latitude component PE of vector FA is therefore FA cos Cu and the distance BA or p along the latitude parallel through the point A is therefore FA sin Cu. The air speed is measured by the air mileage unit AMU which drives the drums H l and 138 at an angular velocity we commensurate with the air speed or wO KOVt when the true air speed is expressed as Vt. As the flight progresses from the point of take-on F along the vector direction FA, the cam I3! is driven through the gear boxes It and I35 to cause a closure of he contact springs IE9 once per nautical mile of flight resulting in the closure of the circuit extending over conductor 250 and to battery through the winding of stepping magnet 238 of the stepping device STP'i-i of Fig. 2 to advance the air miles counter AMC step by step. The pilot noting the reading of the counter at any time and by subtracting therefrom the initial reading asce ain the number of air miles flown. desired, the counter AMC could be provided with a means for resetting it to zero similar, for example, to the resetting knob M2 and resetting gears 25d and 22$ associated with the latitude counter LC so that the air miles flown on any flight could be ascertained directly from the counter without the necessity of making a calculation.

The drum 5!! is driven from the air mileage unit at a rotational speed which is commensurate with the true air speed and during each rotation of the drum, the cam 233 causes sixty closures f the contact springs i3 1. In response to the operation of the flux gate primary transmitter FPT, the synchro-transformer STZ and the amplifier-detector l the difierential relay IE2 is operated causing it to move its armature I63 into engagement with one or the other of the associated contacts thereby causing the establishment of a circuit from ground through one or the other of the field windings of servo-motor SM, through the armature winding of the motor and to battery B.

The motor SM is thereupon operated and through the reduction gear box 59 rotates the shaft it! until, through the gears 58 and !59, the rotor R2 of the synchro-transformer ST2 is so positioned that it receives no potential and the output of the amplifier-detector I55 is thereupon reduced to zero and relay I62 will therefore receive no current. At that time the armature #53 of relay l6! will assume its mid-position thereby opening the circuit of motor SM.

Shaft I56 has now, through the gears 158 and 152', been rotated to assume an angular position corresponding to the true course angle CN and through the disc 155 and crank pin (54 has moved the Scotch yoke U52 to advance the brush H4 in one or the other direction along the surface of the drum to be engaged by the conducting segments of the drum as it rotates. As previously described, as the brush i I 4 moves in one direction towards the upper end of the drum, the number of impulses transmitted over conductor 2I5 will increase and such increase will vary in accordance with the cosine of the angle of the true course flight, or if the brush moves in the other direction towards the lower end of the drum, the number of impulses transmitted over conductor 2! will similarly increase. When the crank pin E54 is vertically above the center of the disc I55, the true flight angle CN is zero and, consequently, the flight course would be due north and the cosine of the true flight course angle would have a maximum value. Therefore, in-this position of the crank pin, the brush IM will be atthe upper end of thedrum III and impulses. at the maximum rate per revolution of the drum will be transmitted to the magnet 204 of the stepping device STPI thereby causing the advance ,of the input wheel of the counter LC.

It has been assumed, however, that the true flight course is in the vector direction FA, as illustrated in Fig. 5, and the course angle is CN and that therefore. the crank pin I54 has been rotated through the angle CN to the position illustrated in Fig. 1, thereby moving the brush II l to the position illustrated. As a consequence the steppin device STPI advances the latitude counter LC at a rate commensurate with the air speed AS and the change in the angle CN of the flight course with respect to north. By reference to the vector diagram of Fig. 5 it will be seen that the vector F'B has the value of FA cos CN but since FA=AS, then FB=ASt cos ON or L=ASt cos Cu. The counter LC is thus operated at such a speed that at any instant it indicates the value of vector FB or the degrees. of latitude.

At the same time the drum 138 has also been rotated at a speed commensurate with the true air speedAS and by the Scotch yoke I53 the brush Hll has been advanced toward the right end of the drum I38 so that the number of impulses generated through the closure of thev cam operated contacts I48 and the engagement of segments of the drum I38with the brush MI, will be in accordance with the air speed and also in accordance with the sine of the flight course angle CN, and may be expressed as AS sin CN. With the brush in the position illustrated impulses are transmitted over conductor 235 and through magnet 224 ofstepping device STPZ whereby the longitude counter LoC is advanced in a positive direction indicative of an eastward flight.

It is to be noted that when the crank pin I54 moves to a position exactly to the right of the center of disc I55 at which position the angle CN is 90 degrees, it moves the brush I41 to the eX- reme right end of the drum. I38in which position the maximum number of impulses are generated by the cam operated contacts I48 and drum segments for each revolution of the drum indicative of a due east flight course.

It is a well known rule of geography that the change in longitude equivalent to a given departure varies in accordance with the sccant of the average latitude angle. The basis for this assertion will be apparent from the following (3.32 c lesion considered in connection with the diaof Fig. 5-. It will be assumed that the longitude of point A with respect to point F is to be d mined. BA are similar arcs or": two circles and are proportional to the radii of such circles. Therefore BA be designated p FE be designated L0 or the lon itude of the point A, then Now the latitude of point A is the angle BGF which is equal to the angle. AOE, butangle AGE 14 is. equal to the angle OAC of the right angle triangleOAC. If now the angle OAC be designated A we have in the triangle OAC,

AC=AO cos A or Substituting Equation Z'in Equation lvwe have =-Lo cost or cos L0= secant A A is the latitude angle so it follows that Now p=FA sin CN but since as previously stated FA ASt then p ASt ON and as the drum I38 rotates at a speed commensurate with the air speed, the impulses generated by the rotation of the. drum and the operation of the cam operated contacts I58 will be in accordance with the value of p. Now to. convert this impulse value of p into the true longitude, the variator SV is provided.

The brush H1301" this variato-r is advanced the drum. I 36 in accordance with the change in the value of the latitude angle A, being positioned at te extreme left end of the drum when the latitude angle is zero and the extreme right end. Whenthe latitude angle. is. 75, degrees. A flight would not be conducted nearer either of the earthspoles than degrees north or south so that values 01" the latitudev angle greater than Eddegrees need not be considered. The secant of the angle L will vary from one to infinity as L increases from 0 to. @fldegrees and refore L0 will vary from the value ,0 to in flnity asjthe latitude angleincreases from O to 9.3 degrees.

From the foregoing, it will be apparent. that theoretically the rate at which stepping iinpulses shouldv be transmitted to the stepping device S'IPil, should be varied from a stepping rate which would advance the. longitude counter one degree for every 60.6681air. miles flown eastward atwtheequator to an infinite stepping rate at poles. This variation in the stepdng rate is made by the secantvariator SV; of the segment I55 of which follows the lunce tion of the angleof latitude A whereoyw "1 the angle of latitude is zero and the brush sitioned at the left end of the drum $69, the nun.- ber of impulses which will be transmitted during each revolution of the drum will be zero since at the same time the brush i l! will be no,- sitioned on the drum I138 so that no segment of the drum will engage it as the drum rotates. As the angle CN increases slightly from 6 so that the brush Hills engaged by one segment during each revolution of the drum, the brush will still be positioned near the left end of drum it?" andsince the drum Itll due to the step-up gear ratio 1' to 6.1 makes about 1 revolution during the passage of each segment of drum M3 past the brush MI; only one or two impulses will be trans mitted to the stepping device STPSZ to advance the counter LoC during each revolution oi drum I38.

As the flight progresses from the point F toward the point A, the value of p will increase and the value of the latitude angle L will increase and consequently the brush ldlrwill move toward the. right end of. the drum I38 to an amount commensurate with the change of value of p or AS: sin CN and the brush I63 will move toward the right end of drum ES!) to an amount cornmensurate with the change in the value of the latitude angle A or the latitude L and the duration of the engagement of brush 53 with the segment 85 or" drum F33 will vary in accordance with the change in the function (secant L). Thus when the flight reaches the point A which the airplane would be required to fly in an eastward direction 52.064 nautical miles for each degree of longitude, the brushes ll and E33 will be positioned as indicated in Fig. 1. With brush Hi3 thus positioned it will be enga ed by the segment H35 during each revolution while the brush i l-l is being engaged by three of the segments of drum I38 and consequently a number of impulses will be transmitted to advance the counter L w ich is commensurate with the function p secant L or impulses generated by the position of brush hit with respect to the drum 538 as modified by the position of brush 583 on the segment G5.

If the flight course had been flown from point F to point G, the value of p would further decrease and the value of the latitude angle L would increase from 0 to 75 degrees and consequently the brush 1 4| would have moved nearly to the extreme right end of the drum I38 to an amount commensurate with the value of p or ASt sin CN and the brush I53 would have moved to the extreme right end of drum IGD commensurate with the latitude angle x or the latitude L and the engagement of brush N33 with the segment 185 of drum Hill would have lasted during each entire revolution of drum I68 and while the drum I38 and associated contact springs I48 were generating a number of impulses per revolution of drum I38 somewhat less than sixty impulses per revolution. Thus a larger number of impulses would have been transmitted to the stepping device STP2 during the time that the flight is proceeding from A to G. It will thus be apparent that the nearer the pole the flight proceeds, the faster will be the stepping speed i of the stepping device STPZ.

While the functioning of the invention for a north eastward flight has been discussed, it is believed that its operation on a flight southward above the equator and in the east hemisphere will be apparent. On a flight into the western hemisphere either after flying eastwardly across the 180-degree reference meridian or westerly across the O-degree reference meridian the pilot will operate the key K2 when the fl ght crosses either reference meridian. On a flight eastward of the reference meridian but south of the equator, he will operate the key Kl when the equator is crossed and on a flight in the southern hemisphere but westward, from the 0-degree reference meridian or eastwardly across the 180- degree reference meridian, he will also operate key K2 when the reference meridians are crossed. Conversely, if a flight is conducted from the western hemisphere easterly across the O-degree reference meridian or Westerly across the 180- degree reference meridian into the eastern hemisphere, the pilot will restore the key K2 to its normal position.

What is claimed is:

1. In an automatic dead-reckoning device for a craft, a latitude indicator, a drum, means for rotating said drum at a speed commensurate with the speed of travel of said craft, two groups of conducting segments extending respectively from the central portion of said drum axially toward the ends of said drum and insulatedly mounted on said drum with the apices of the segments of one group positioned spirally around said drum and with the apices of the segments of the other group positioned along a reversed spiral around said drum whereby the apices of successive corresponding segments of said groups are axially spaced at equally increasing distances from each other, a brush engageable with either group of said segments and movable axially along the surface of said drum in accordance with the cosine of the true course angle of the travel of said craft to cause the generation of a varying number of impulses during each revolution of said drum, and a two-way stepping device responsive to impulses generated by the engagement of said brush with one or the other of said groups of segments for operating said latitude indicator in one or the other direction.

2. In an automatic dead-reckoning device for a craft, a latitude indicator, a drum, means for rotating said drum at a speed commensurate with the speed of travel of said craft, a plurality of substantially similar tapering conducting segments insulatedly mounted on the surface of said drum With their apices positioned spirally around said drum and their widest portions positioned adjacent to one end of said drum, a brush engageable with said segments and movable axially along the surface of said drum in accordance with the cosine of the true course angle of the travel of said craft whereby said brush is engaged by varying numbers of said segments and for varying durations during each revolution of said drum, an interrupter driven by said drum and operable to render said brush effective a plurality of times during each revolution of said drum, a stepping device for operating said latitude indicator and an operating circuit for said stepping device controlled jointly by said interrupter and by the engagement of said brush with the segments of said drum.

3. In an automatic dead-reckoning device for a craft, a longitude indicator, an impulse generator, means for driving said generator at a speed commensurate with the speed of travel of said craft, means for varying the number of impulses generated during each revolution of said generator in accordance with the sine of the true course angle of the travel of said craft, means for further varying the number of impulses transm' ted from said generator in accordance with the secant of the angle of latitude of the course of said craft, and a stepping device responsive to said generated impulses as thus transmitted for operating said longitude indicator.

4. In an automatic dead-reckoning device for a craft, a longitude indicator, a drum, means for rotating said drum at a speed commensurate with the speed of travel or" said craft, two groups of conducting segments extending respectively from the central portion of said drum axially toward the end of said drum and insulatedl mounted on said drum with the apices of the segments of one group positioned spirally around said drum and with the apices of the segments of the other group positioned along a reverse spiral around said drum whereby the apices of successive corresponding segments of said groups are axially spaced equally increasing distances from each other, a brush engageable with either group of said segments and movable axially along the surface of said drum in accordance with the sine of the true course angle of the travel of said craft 17 to enable the generation of a varying number of impulses during each revolution of said drum, means for further varying the number of said impulses in accordance with the secant of the angle of latitude of the course of said craft, and a two-way stepping device responsive to the impulses generated by the engagement of said brush with one or the other of said roups of segments and as further modified by said latter means for operating said longitude indicator in one or the other direction.

5. In an automatic dead-reckoning device for a craft, a longitude indicator, a drum, means for rotating said drum at a speed commensurate with the speed of travel of said craft, a plurality of substantially similar tapering conducting segments insulatedly mounted on the surface of said drum with their apices positioned spirally around said drum and their widest portions positioned adjacent to one end of said drum, a brush engageable with said segments and movable axially along the surface of said drum in accordance with the sine of the true course angle of the travel of said craft whereby said brush is engaged by varying members of said segments and for varying durations during each revolution of said drum, an interrupter driven by said drum and operable to render said brush effective a plurality of times during each revolution of said drum, means for further rendering said brush effective for intervals varying in accordance with the secant of the latitude of the course of said craft, a stepping device for operating said longitude indicator, and an operating circuit for said stepping device controlled jointly by said interrupter, by said latter means and by the engagement of said brush with the segments of said drum.

6. In an automatic dead-reckoning device for a craft, a longitude indicator, a drum, means for rotating said drum at a speed commensurate with the speed of travel of said craft, a plurality of conducting segments extending axially along the surface of said drum and insulatedly mounted thereon with their apices positioned spirally around said drum, a brush engageable with said segments and movable axially along the surface of said drum in accordance with the sine of the sourse angle of the travel of said shaft to enable the generation of a varying number of impulses during each revolution of said drum, a second drum driven from the shaft of said first drum at a speed greater than the speed of said first drum, a conducting segment on said latter drum contoured in accordance with a secant function, a brush movable axially over the surface of said second drum in accordance with the latitude of the course of said craft whereby the circuit closure between said drum segment and said brush is caused to vary in accordance with the secant of the latitude, a stepping device for operating said longitude indicator, and a circuit for said stepping device jointly controlled by 18 the engagement of the brushes with the segments of their respective drums whereby said longitude indicator is advanced at a rate determined by the course angle modified by the sine of the course speed and further modified by the secant of the angle of latitude.

7. In an automatic dead-reckoning device for a craft, a longitude indicator, a drum, means for rotating said drum at a speed commensurate with the speed of travel of said craft, a plurality of identical tapering conductive segments insulatedly mounted on the surface of said drum with their apices positioned spirally around said drum and their widest portions positioned adjacent to one end of said drum, a brush engageable with said segments and movable axially along the surface of said drum in accordance with the sine of the true course angle of the travel of said craft whereby said brush is engaged by varying numbers of said segments and for varying durations during each revolution of said drum, an interrupter driven by said drum and operable to render said brush effective a plurality of times during each revolution of said drum, a second drum driven from the shaft of said first drum at a speed such that said drum makes substantially as many revolutions during one revolution of said first drum as there are segments on said first drum, a conducting segment on said second drum contoured in accordance with a secant function, a brush movable axially over the surface of said second drum in accordance with the latitude of the course of said craft whereby the circuit closure between said drum segment and said brush is caused to vary in accordance with the secant of the latitude, a stepping device for operating said longitude indicator, and a circuit for said stepping device jointly controlled by the engagement of the brushes with the segments of their respective drums and by said interrupter whereby said longitude indicator is advanced at a rate determined by the course speed modified by the sine of the course angle and further modified by the secant of the angle of latitude.

WALTER P. ALBERT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,101,128 Jensen et al June 23, 1914 1,704,250 Holmes Mar. 5, 1929 1,802,963 Young Apr. 28, 1931 1,976,617 Lake et al Oct. 9, 1934 2,022,275 Davis Nov. 26, 1935 2,073,246 Merrick Mar, 9, 1937 FOREIGN PATENTS Number Country Date 244,013 Germany June 3, 1909 

